Impedance data as a possible basis for finding stability constants of cucurbituril complexes with inorganic cations

An analysis of the array of impedance data for the interface the Hg-electrode/salt solutions of macrocyclic cavitands of the cucurbituril family containing their supramolecular cationic complexes was performed. A significant change in the properties of the adsorption layer was established with a change in the charge of the electrode surface and the concentrations of the components of the complex formation reaction. The existence of two types of adsorption layer was found, one of which (with positive charges on the electrode surface) is formed with the participation of neutral cavitand molecules. The high sensitivity of the impedance data to the presence of these molecules in solution made it possible to establish the corresponding quantitative dependences for systems with known values of the stability constants of cationic complexes. It is shown that these data can be used to find previously unknown stability constants of cationic complexes of a given cavitand formed in other similar salt systems. The applicability of the proposed method was demonstrated using impedance data for systems with known stability constants of cationic complexes (cucurbit[6]uril + Me2 SO4, Me+ = K+, Na+).